Re-circulating spray wind tunnels typically use a droplet extractor to restrict droplets from re-circulating through the tunnel. The droplets extracted from the airflow by the droplet extractor typically are collected in a droplet extractor reservoir from which the collected droplets (i.e., liquid waste) are drained into a drain line, liquid trap, or waste container. However, the droplet extractor can cause issues with the flow of liquid waste out of the droplet extractor reservoir because of differential pressure between the wind tunnel and the drain line, liquid trap, or waste container. In some cases, the differential pressure can cause the liquid waste to not drain out of the droplet extractor reservoir, resulting in the liquid waste overflowing out of the reservoir and into the wind tunnel.
To accommodate for the differential pressure, some wind tunnel operators fix the drain line, liquid trap, or waste container at an orientation that is specific to the wind tunnel operating condition (e.g., wind speed). The orientation is set such that the liquid waste drains from the droplet extractor reservoir for the specific wind tunnel operating condition, and this set point is not changed during operation of the wind tunnel.